The present invention relates to charge emitters, and more particularly, to a novel field emitter with a substantially constant field emission current.
Field emission devices (hereinafter referred to as xe2x80x9cFED""sxe2x80x9d) are well known in the art and are commonly employed for a broad range of applications including image display devices. An example of a FED is described in U.S. Pat. No. 5,142,184 issued on Aug. 25, 1992. Prior FED""s typically have a cathode or emitter that is utilized to emit charges that are attracted to a distally disposed anode. A voltage differential is created between the emitter and an extraction grid or gate in order to facilitate charge emission from the emitter. Often, arcing or breakdown occurs between the emitter and the gate causing large current flow through the emitter. The breakdown can result from, among other things, an inefficient vacuum or from insufficient distance between the emitter and the gate. The breakdown generally damages or destroys the emitter.
Further, charge emission from a FED is generally a function of time. An example is the use of an FED to generate a grey scale wherein the gate of the FED is pulse width modulated. However, FED""s used in these applications have traditionally been plagued by current runaway and unwanted discharges from the cathode to the anode that cause catastrophic damage to the device, especially in display applications. The common solution to this problem is to use a resistive ballast (in series with the cathode or emitter) to control the gate voltage. This solution, however, is only partially effective and negatively impacts FED efficiency and cost.
Accordingly, it is desirable to have a field emission device that prevents damaging the emitter during breakdown between the emitter and gate, and that substantially prevents breakdown between the emitter and gate.
To achieve the objects and advantages specified above and others, an electronic circuit apparatus for a charge emission device is disclosed. In the preferred embodiment, the apparatus includes a field emission device electrically connected to a charge ballast electronic circuit, wherein the charge ballast electronic circuit includes a capacitance device electrically connected in parallel with a resistor. Further, an electronic switch is electrically connected in series with the capacitance device. The electronic switch allows the field emission device to emit electrons while the capacitance device charges to a voltage. As the capacitance device charges, the charge emission decreases.